Gamara IIThis is exactly what I spent my adolescence doing, and it was pretty fantastic.

One time one of the employees (at Burger King, coincidentally), left their headset on the counter while we were there, my friend "borrowed" it, and sweet chaos ensued over the next several days before they changed the frequencies. Sadly we had not the wisdom to record it. Eventually they got wise to the game and just started taking orders at the window, which ended up taking them 10x longer.